An EUV (Extreme Ultra-Violet) exposure apparatus is an apparatus which reduces and projects a micro-pattern formed on a reticle onto resist on a wafer by using an EUV light beam. During the performing of the EUV exposure, an organic material as a resist material is decomposed by energy of the EUV irradiation light beam, so that a portion of decomposition products called an out-gas is emitted into the EUV exposure apparatus. The emitted decomposition product is adhered on a mirror in the EUV exposure apparatus, and thus, the mirror is hazed, so that reflectance of the mirror is decreased. Therefore, illuminance of the EUV light beam irradiated on the resist film on the wafer is deteriorated. As a result, there is a problem in that an exposure rate is decreased and productivity is decreased.
As a method of removing the haze of the mirror, a gas or a radical is supplied into the exposure apparatus. However, in this method, the adhesion material cannot be efficiently removed. Therefore, a technique for efficiently removing the adhered material adhered on the mirror is preferred.